1. Field of the Invention
The present invention relates to novel 2-methylthioethyl-substituted heterocycles, their derivatives, method of production and use as feed additive.
2. Description of the Related Art
Essential amino acids such as methionine, lysine or threonine are, as feed additives, very important components of animal nutrition. Their supplementation makes possible, firstly, more rapid growth of the animals, but secondly also more efficient feed utilization. This is a great economic advantage. The markets for feed additives are of great industrial and economic importance. In addition, they are strong growth markets due, not least, to the increasing importance of countries such as, for example, China and India.
WO 2004008874 discloses, inter alia, that methionine (2-amino-4-methylthiobutyric acid) is the first limiting amino acid for many animal species. For instance, in dairy cattle, for example, efficient milk production with respect to the amount and quality is greatly dependent on a sufficient feed of methionine. The methionine requirement of high-performance dairy cattle cannot be covered in this case by the microbial protein formed in the rumen or by protein from the feed which is not broken down in the rumen (Graulet et al., J. Animal and Feed Sciences (2004), 269). It is therefore advantageous to supplement methionine to the feed in order to increase the economic efficiency of milk production and quality of the milk.
In the case of monogastric animals such as, for example, poultry and pigs, D,L-methionine and the Methionine Hydroxy Analog (MHA) having the chemical name D,L-2-hydroxy-4-methylthiobutyric acid (HMB), are conventionally used as feed additives. The available amount of L-methionine is thereby increased in the organism which is then available to the animal for growth.
In contrast thereto, supplementation of the feed with methionine is not effective in ruminants, since the majority is broken down by microbes in the rumen of ruminants. Owing to this breakdown, therefore, only a fraction of the supplied methionine passes into the small intestine of the animal, where generally the methionine is absorbed into the blood.
WO 99/04647 describes the use of MHA for ruminants. Therein it is asserted that MHA is only partly broken down in the rumen and therefore at least 20-40% of the supplemented MHA, after absorption in the small intestine, can pass into the metabolism. In numerous other publications, in contrast, the mode of action of MHA in ruminants is discussed differently. Thus, for example, WO 200028835 describes that MHA can only successfully pass through the rumen and finally arrive in the small intestine for absorption when MHA is administered in very large amounts of 60-120 g/day/animal. However, this is no longer economically efficient.
In order that methionine products such as D,L-methionine or rac-MHA are available to ruminants with high efficiency, a form protected from rumen breakdown must be used. The challenge in this case is to find a suitable methionine product which gives the methionine a rumen stability which is as high as possible and nevertheless ensures high and efficient absorption of the methionine in the intestine. In this case there are a plurality of possibilities of giving the D,L-methionine or rac-MHA these properties:
a) Physical Protection:
By applying a suitable protective layer or distributing the methionine in a protective matrix, a high rumen stability can be achieved. As a result the methionine can pass through the rumen virtually without loss. In the further course, the protective layer is then opened or removed, for example, in the abomasum by acid hydrolysis and the released methionine can then be absorbed by the animal in the small intestine. The protective layer or matrix can consist of a combination of a plurality of substances such as, for example, lipids, inorganic materials and carbohydrates. For example, the following product forms are commercially available:
i) Met-Plus™ from Nisso America, is a lipid-protected methionine having a D,L-methionine content of 65%. The protective matrix consists of the calcium salts of long-chain fatty acids such as, for example, lauric acid. Butylated hydroxytoluene acts as preservative.
ii) Mepron® M85 from Degussa AG is a carbohydrate-protected methionine which has a core of D,L-methionine, starch and stearic acid. Ethylcellulose is used as protective layer. The product has a content of 85% D,L-methionine.
iii) Smartamine™ M from Adisseo is a polymer-protected methionine. The pellets, in addition to stearic acid, contain at least 70% D,L-methionine. The protective layer contains vinylpyridine-styrene copolymer.
Although physical protection prevents the microbial breakdown of methionine in the rumen and as a result the supply and utilization of methionine can be increased in the animal, there are some serious disadvantages.
The production or coating of methionine is usually a technically complicated and complex process and is therefore expensive. In addition, the surface coating of the finished pellets can easily be damaged by mechanical stress and abrasion during feed administration, which can lead to reduction or complete loss of the protection. Therefore, it is also not possible to process the protected methionine pellets into a larger mixed-feed pellet and repellet them, since as a result, again the protective layer would break up by the mechanical stress. This greatly restricts the use of such products, since the mixed feed pelletting is a widespread method of feed processing.
b) Chemical Protection:
Increased rumen stability of methionine can, in addition to the purely physical possible methods of protection, also be achieved by modifying the chemical structure, for example by esterifying the carboxylic acid group. Currently, the following products are commercially available or are described in the literature:
i) Methionine esters such as, for example, D,L-tert-butylmethionine: The esters were tested and demonstrated only moderate rumen stability (Loerch and Oke; “Rumen Protected Amino Acids in Ruminant Nutrition” in “Absorption and Utilization of Amino Acids” Vol. 3, 1989, 187-200, CRC Press Boca Raton, Fla.). For D,L-tert-butylmethionine, in contrast, in WO 0028835, a biological value of 80% was published.
ii) Metasmart™ from Adisseo is the racemic isopropyl ester of MHA (HMBi). This compound is also marketed under the trademark “Sequent” by the American company Novus. WO 00/28835 published a biological value of at least 50% for HMBi in ruminants. In this case, especially, the surprisingly rapid absorption of the hydrophobic HMBis through the rumen wall plays a decisive role. The ester can then be hydrolyzed to MHA in the blood and, after oxidation and subsequent transamination, converted to L-methionine. Patent EP 1358805 published a comparable biological value for HMBi. In these studies, HMBi was applied to a porous carrier. In a further publication, the European Commission reported that again approximately 50% HMBi is absorbed through the rumen wall (European Commission: Report of the Scientific Committee on Animal Nutrition on the Use of HMBi; 25 Apr. 2003). Graulet et al. published in 2004 in the Journal of Animal and Feed Science (269), the fact that via the lipophilic properties of the isopropyl group of HMBi, better diffusion through the rumen wall is made possible.
For the production of HMBi, two different processes have been published. For instance, HMBi, on the one hand, can be synthesized directly in one stage from the corresponding cyanohydrine (WO 00-59877). The esterification to give the isopropyl ester proceeds in this case in situ, without MHA having to be isolated in advance. Another process, in contrast, esterifies pure MHA with isopropanol (WO 01-58864 and WO 01-56980). In both cases, for the synthesis, Prussic acid is used which is expensive and, in addition, involves a great hazard potential.
The aquafarming sector (Food and Agriculture Organization of the United Nation (FAO) Fisheries Department “State of World Aquaculture 2006”, 2006, Rome. International Food Policy Research Institute (IFPRI) “Fish 2020: Supply and Demand in Changing Markets”, 2003, Washington, D.C.) has also recently acquired importance. The culture of edible saltwater and freshwater animals, in particular fish and crustacea, likewise requires particular product forms for supply with methionine.
The supply of fish and crustacea which are held commercially in aquacultures, requires a correspondingly protected product form, firstly in order that the product during feed administration remains sufficiently stable in the aqueous environment and secondly in order that the methionine product finally taken up by the animal can be optimally utilized in the animal organism.